Synthesis, characterization, and antimicrobial properties of two cu(II) complexes derived from a benzimidazole ligand

Article abstract of DOI:10.1080/00958972.2014.940924

Two copper(II) complexes, [Cu(L)₂](ClO₄)₂] and [Cu(L)(bipy)](ClO₄)₂, were prepared and characterized by the spectroscopic and analytic methods, where L is N-butylbenzimidazole and bipy is 2,2’-bipyridine. Single crystals of [Cu(L)(bipy)](ClO₄)₂ suitable for X-ray diffraction study were obtained by slow diffusion of diethyl ether into a DMF solution of the complex and the complex was found to crystallize as [Cu(L)(bipy)](ClO₄)₂·DMF. The asymmetric unit contains one [Cu(L) (bipy)]²⁺, two uncoordinated perchlorates, and one DMF solvate. Coordination geometry around Cu (II) is distorted square pyramidal with τ value of 0.31. Thermal properties of the complexes were examined by thermogravimetric analysis, indicating that the complexes are thermally stable to 310°C. The metal complexes were screened for their in vitro antibacterial and antifungal activities Bacillus subtilis and Bacillus cereus (as Gram(+) bacteria), Escherichia coli, Enterobacter aerogenes, and Klebsiella pneumoniae (as Gram(–) bacteria), and Saccharomyces cerevisiae, Candida utilis, and Candida albicans (as yeasts). The complexes show antibacterial and antifungal activities against bacteria and yeasts.

Full text of DOI:10.1080/00958972.2014.940924

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Synthesis, characterization, and
antimicrobial properties of two
Cu(II) complexes derived from a
benzimidazole ligand
a
Muhammet Kose
a
Department of Chemistry, K. Maras Sütçü İmam University,
Kahramanmaraş, Turkey
Accepted author version posted online: 02 Jul 2014.Published
online: 25 Jul 2014.
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To cite this article: Muhammet Kose (2014) Synthesis, characterization, and antimicrobial
properties of two Cu(II) complexes derived from a benzimidazole ligand, Journal of Coordination
Chemistry, 67:14, 2377-2392, DOI: 10.1080/00958972.2014.940924
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Journal of Coordination Chemistry, 2014
Vol. 67, No. 14, 2377–2392, http://dx.doi.org/10.1080/00958972.2014.940924
Synthesis, characterization, and antimicrobial properties of
two Cu(II) complexes derived from a benzimidazole ligand
MUHAMMET KOSE*
Department of Chemistry, K. Maras Sütçü İmam University, Kahramanmaraş, Turkey
(
Received 21 March 2014; accepted 4 June 2014)
Two copper(II) complexes, [Cu(L)
terized by the spectroscopic and analytic methods, where L is N-butylbenzimidazole and bipy is
,2′-bipyridine. Single crystals of [Cu(L)(bipy)](ClO suitable for X-ray diffraction study were
obtained by slow diffusion of diethyl ether into a DMF solution of the complex and the complex
was found to crystallize as [Cu(L)(bipy)](ClO ·DMF. The asymmetric unit contains one [Cu(L)
2 4 2 4 2
](ClO ) ] and [Cu(L)(bipy)](ClO ) , were prepared and charac-
2
4 2
)
4 2
)
2+
(
bipy)] , two uncoordinated perchlorates, and one DMF solvate. Coordination geometry around Cu
(
II) is distorted square pyramidal with τ value of 0.31. Thermal properties of the complexes were
examined by thermogravimetric analysis, indicating that the complexes are thermally stable to
10 °C. The metal complexes were screened for their in vitro antibacterial and antifungal activities
3
Bacillus subtilis and Bacillus cereus (as Gram(+) bacteria), Escherichia coli, Enterobacter aeroge-
nes, and Klebsiella pneumoniae (as Gram(–) bacteria), and Saccharomyces cerevisiae, Candida
utilis, and Candida albicans (as yeasts). The complexes show antibacterial and antifungal activities
against bacteria and yeasts.
Keywords: Cu(II) complex; Benzimidazole; 2,2′-Bipyridine; X-ray structure; Antimicrobial
1. Introduction
Benzimidazole is a hetero bicyclic aromatic compound containing a phenyl ring fused to an
imidazole ring [1]. Benzimidazole and its derivatives are of wide interest due to their bio-
logical activities and clinical applications [2, 3]. Some benzimidazole compounds have been
reported to show pharmacological activities such as antiviral, antibacterial, antifungal, and
*
Email: muhammetkose@ksu.edu.tr
2014 Taylor & Francis
©

2
378
M. Kose
1
Figure 1. H NMR spectrum of L.
antimalarial [4–7]. Benzimidazoles are generally synthesized by the condensation of
o-phenylenediamine with carboxaldehydes, carboxylic acids, or their derivatives [8, 9].
N-substituted benzimidazole derivatives are synthesized by reaction with alky/aryl halide in
the presence of base. Several benzimidazole derivatives were synthesized by derivatization
at the N–H group [10–12]. Transition metal complexes of 2,6-bis-(benzimidazol-2-yl)-pyri-
dine (bzimpy) (figure 1) were synthesized and their properties were extensively investigated
[
13–18].
The biological activity and pharmacological properties of benzimidazole derivatives have
led us to investigate the coordination behavior of benzimidazole ligands towards transition
metal ions. In this study, two Cu(II) complexes of an N-butylbenzimidazole ligand (L) were
prepared and characterized by analytical and spectroscopic methods.
2
2
. Experimental
.1. General methods
All starting materials and organic solvents were purchased from commercial sources and
used as received, unless noted otherwise. IR spectra were performed using KBr pellets on a
Perkin Elmer Paragon 1000PC. CHN analysis was performed using a CE-440 elemental

Cu(II) benzimidazole complexes
2379
1
13
analyzer. H and C NMR spectra were obtained using a Bruker Avance 400. ESI mass
spectra were recorded on a Thermo Fisher Exactive + Triversa Nanomate mass spectrometer.
Electronic spectra from 200 to 900 nm were obtained on a Shimadzu UV-1800 UV–vis
spectrophotometer. Thermal analyses of the complexes were performed on a Perkin Elmer
−
1
Pyris Diamond DTA/TG Thermal System under nitrogen at a heating rate of 20 °C min .
Data collection and cell refinement for X-ray crystallography were completed using a
Bruker APEX2 CCD diffractometer and data reduction was performed using Bruker
SAINT. SHELXTL was used to solve and refine the structures [19].
2
.2. X-ray structures solution and refinement for [Cu(L)(bipy)](ClO ) ∙DMF
4 2
3
A single crystal of dimensions 0.39 × 0.13 × 0.09 mm was chosen for the diffraction experi-
ment. X-ray diffraction data were collected at 150(2) K on a Bruker ApexII CCD diffrac-
tometer using Mo-Kα radiation (γ = 0.71073 Å). The structure was solved by direct
2
methods and refined on F using all the reflections [20]. All non-hydrogen atoms were
refined using anisotropic atomic displacement parameters and hydrogens were inserted at
Table 1. Crystallographic data.
Complex
Empirical formula
Formula weight
Crystal size/color
Crystal system
Space group
Unit cell
[Cu(L)(bipy)](ClO
44Cl Cu N
915.27
0.39 × 0.13 × 0.09/green
Triclinic
4 2
) ·DMF
O
8 9
40
C H
2
P-1
a (Å)
b (Å)
c (Å)
α (°)
β (°)
γ (°)
Volume (Å )
Z
9.4101(6)
11.0932(7)
20.5323(12)
93.8370(10)
100.1520(10)
95.6090(10)
2091.9(2)
2
3
−
1
Abs. coeff. (mm
)
0.714
Refl. collected
25,160
Ind. Refl. [Rint
]
8574 [0.0335]
0.0375, 0.0933
0.0496, 0.1015
984,504
R
R
1
, wR
, wR
2
[I > 2σ (I)]
(all data)
1
2
CCDC
Table 2. Selected bond lengths [Å] and angles [°] for [Cu(L)(bipy)](ClO
4
)
2
·DMF.
1.9885(17)
Cu(1)–N(2)
Cu(1)–N(3)
Cu(1)–N(4)
2.0069(18)
1.9625(17)
2.0075(18)
Cu(1)–N(6)
Cu(1)–N(7)
2.2540(19)
N(2)–Cu(1)–N(3)
N(2)–Cu(1)–N(4)
N(2)–Cu(1)–N(6)
N(2)–Cu(1)–N(7)
N(3)–Cu(1)–N(4)
79.74(7)
157.03(7)
99.65(7)
87.06(7)
80.11(7)
N(3)–Cu(1)–N(6)
N(3)–Cu(1)–N(7)
N(4)–Cu(1)–N(6)
N(4)–Cu(1)–N(7)
N(6)–Cu(1)–N(7)
175.75(7)
106.16(7)
99.63(7)
109.13(7)
77.97(7)

2
380
M. Kose
calculated positions using a riding model. Details of the crystal data and refinement are tab-
ulated in table 1. Selected bond lengths and angles for the complex are presented in table 2.
2
.3. Synthesis of 2,6-bis-(benzimidazol-2-yl)-pyridine (bzimpy)
2
,6-Bis-(benzimidazol-2-yl)-pyridine (bzimpy) was synthesized by the literature method
1
[
21]. Yield: 68%. Colorless; NMR: (DMSO as solvent, ppm, H) 7.31 (t, 4H, CH aromatic),
7
.76(d 4H CH aromatic), 8.16 (t 1H CH aromatic), 8.34 (d 1H CH aromatic). IR (KBr, ν,
−
1
−1
cm ): 3193, 1601, 1573, 1318, 1278, 1230, 819, 738 cm . Mass spect. (ESI): m/z 312
+
+
[L + H] (100%), 334 [L + Na] (30%).
2
.4. Synthesis of L
N-butylation of 2,6-bis(benzimidazol-2′-yl)pyridine (bzimpy) was prepared by a slight vari-
ation of a reported general N-alkylation method [22]. Bzimpy (1.00 g, 3.2 mM) and NaOH
(
(
0.50 g, 12.8 mM) were stirred for 4 h at 60 °C. To the stirring solution, 1-bromobutane
1.30 g, 9.6 mM) was added in excess and stirred for two days at 60 °C. The solvent was
removed on a rotary evaporator to give white–yellow residue. Chloroform (20 mL) was
added to the residue and the precipitated NaBr was removed by filtration. Evaporation of
the chloroform yielded a cream-colored product. Yield: 1.05 g, 78% (based on bzimpy).
Elemental analysis data: Anal. (%) calculated for C H N (423.55): C, 76.56; H, 6.90; N,
2
7 29 5
1
1
6
6.53. Found (%): C, 76.28; H, 6.65; N, 16.37. H NMR: (CDCl as solvent, ppm,), 0.71 (t
3
H CH –C), 1.35 (s (sextet) 4H C–CH –C), 4.73 (t 4H C–CH –C), 1.72(q (quintet) 4H C–
3
2
2
CH –), 7.37–7.47 (t 4H CH aromatic), 7.89(d 4H CH aromatic), 8.06 (t 1H CH aromatic),
2
1
3
8
.33 (d 1H CH aromatic). C NMR (CDCl –d as solvent, ppm): 13.48, 19.85, 32.12,
3 6
4
4.64 (aliphatic), 110.39, 120.34, 122.71, 123.47, 125.50, 136.31, 138.11, 142.86, 150.57
−
1
(aromatic). IR (KBr, ν, cm ): 2956, 2929, 2871, 1595, 1434, 1410, 1571, 1328, 1285,
−1
+
1
249, 1178, 1076, 993, 823, 740, 660, 581 cm . Mass spect. (ESI): m/z 424 [L + H]
+
+
+
(
100%), 446 [L + Na] (15%), 847 [(L) + H] (15%), 869 [(L) + Na] (10%).
2 2
2
.5. Preparation of [Cu(L) ](ClO ) ]
2 4 2
Cu(ClO ) ·6H O (0.37 g, 1 mM) in MeOH (10 mL) was added to a refluxing solution of
4
2
2
the ligand (0.84 g, 2 mM) in MeOH (50 mL). The reaction solution was refluxed for 4 h and
cooled to room temperature. Green precipitate formed was collected and washed with
diethyl ether (20 mL). Single crystals of the complex were obtained via the vapor diffusion
method (DMF-diethyl ether); but, due to their small size and very weak diffraction, the
2
+
data-set was not collected. Yield: 0.86 g, 78% (based on Cu ) Color: green. m.p. decom-
pose 310–320 °C. Elemental analysis data: Anal (%) calculated for C H CuCl O
2 8
5
4
58
(
1108.55): C, 58.45; H, 5.23; N, 12.63. Found (%): C, 57.97; H, 5.17; N, 12.52. IR (KBr,
−1
ν, cm ): 2960, 2871, 2868, 1601, 1571, 1515, 1481, 1462, 1416, 1333, 1201, 1073, 911,
8
(
(
−
1
64, 808, 743, 692, 620, 567, 494, 482, 468, 432, 399 cm . Mass spect. (ESI): m/z 1008
+
+
+
65%) [Cu(L) ](ClO ) , 585(20%) [Cu(L)(ClO )] , 486(35%) [Cu(L)] , 454(100%) [Cu
2 4 4
L) ] .
2
2
+
*
Caution: Perchlorate salts of metal complexes are potentially explosive and must be
handled with care.

Cu(II) benzimidazole complexes
2381
2.6. Preparation of [Cu(L)(bipy)](ClO4)2
Cu(ClO ) ·6H O (0.37 g, 1 mM) in MeOH (10 mL) was added to a refluxing solution of L
4
2
2
(0.42 g, 1 mM) in MeOH (50 mL). When addition was completed, the green solution was
refluxed for 2 h and then 2,2′-bipyridine (bipy) (0.16 g, 1 mM) was added. The reaction
mixture was further refluxed for 4 h and cooled to room temperature. Green precipitate was
collected and washed with MeOH (20 mL) and diethyl ether (20 mL). Single crystals suit-
able for X-ray diffraction study were grown by diffusion of diethyl ether into a DMF solu-
2
+
tion of the complex. Yield: 0.66 g, 77% (based on Cu ). Color: green. m.p. 310–320 °C
(
decomp.). Elemental analysis data: Anal (%) calculated for C H CuCl N O (842.18): C,
2.77; H, 4.43; N, 11.64. Found (%): C, 52.37; H, 4.21; N, 11.43. IR (KBr, ν, cm ): 2960,
37 37 2 7 8
−
1
5
2
6
930, 2871, 1599, 1572, 1483, 1433, 1332, 1198, 1133, 1088, 1008, 918, 867, 749, 660,
+
22, 481, 427. Mass spect. (ESI): m/z 742.69 (35%), [Cu(L)(bipy)](ClO ) , 321(100%) [Cu
4
2
+
+
(L)] , 486(10%) [Cu(L)] .
2
.7. Biological properties
The growth in antimicrobial activities of the complexes were tested against five bacteria
Bacillus subtilis IMG22, Bacillus cereus EU, Klebsiella pneumoniaee FMC 5, Escherichia
(
coli DM, and Enterobacter aerogenes (Clinic izolate)) and three yeasts (Candida albicans
ATCC 1023, Candida utilis NRRL-Y-900, and Saccharomyces cerevisiae WET 136). These
micro-organisms were provided from the Microbiology Laboratory Culture Collection,
Department of Biology, Kahramanmaraş Sütçü İmam University, Turkey.
Antimicrobial activities of the complexes were determined using hollow agar, as
described below. The bacteria were first incubated at 37 ± 0.1 °C for 24 h in nutrient broth
(Difco), and the yeasts were incubated in sabouraud dextrose broth (Difco) at 25 ± 0.1 °C
for 24 h. The cultures of the bacteria and yeast were injected into Petri dishes (9 cm) in the
8
6
amount of 0.1 mL (Mc Farland OD: 0.5, 1.5 × 10 bacteria/mL and 1.5 × 10 yeast/mL).
Then, Mueller Hinton agar and sabouraud dextrose agar (sterilized in a flask and cooled to
4
2
5–50 °C) were homogeneously distributed onto the sterilized Petri dishes in the amount of
5 mL. Subsequently, the complex 70 microliters (700 μg) in MeOH was pipetted into the
hollow agar. In addition, blank paper disks treated with antibacterial ampicillin (10 μg) and
antifungal nystatin 100U were used as positive controls. The plates combined with the disks
were left at 4 °C for 2 h; the plates injected with yeast were incubated at 25 ± 0.1 °C for 24
h, and those injected with bacteria were incubated at 37 ± 0.1 °C for 24 h. After 24 h, inhibi-
tion zones appearing around the disks were measured and recorded in mm [23, 24].
2
.8. Determination of minimal inhibitory concentration
A micro-dilution broth susceptibility assay was used, as recommended by NCCLS, for
determination of the minimal inhibitory concentration (MIC) of the complex. All tests were
performed in Mueller Hinton broth (MHB) supplemented with Tween 80 detergent (final
concentration of 0.5% (v/v)), with the exception of the yeasts (sabouraud dextrose broth
(SDB) + Tween 80). Bacterial strains were cultured overnight at 37 °C in MHB, and the
yeasts were cultured overnight at 25 °C in SDB. Geometric dilutions ranging from 100 to
−
1
8
8
00 μg mL of the complexes were prepared including one growth control (MHB + Tween
0) and one sterility control (MHB + Tween 80 + test oil). Test tubes were incubated under

2
382
M. Kose
OH
OH
N
H
N
H
N
O
O
CH3(CH2)2CH2Br
H PO4
N
3
N
N
N
N
N
+
NaOH
THF 70 °C
2
30 °C
N
N
NH2
NH2
bzimpy
L
Scheme 1. Synthesis of L.
normal atmospheric conditions at 37 °C for 24 h for bacteria and at 25 °C for 48 h for the
yeasts. The microbial growth was determined by turbidimetric methods.
3. Results and discussion
3.1. Synthesis of L
2
,6-Bis(benzimidazole-2′-yl)pyridine (bzimpy) was prepared by the reaction of 2,6-pyri-
dinedicarboxylic acid with o-phenylenediamine in syrupy phosphoric acid at 230 °C [21].
L was synthesized by the reaction of 1-bromobutane and bzimpy in the presence of a
13
Figure 2.
C NMR spectrum of L.

Cu(II) benzimidazole complexes
2383
Figure 3. ESI mass spectrum of L.
base (NaOH) in THF. Synthesis of L is illustrated in scheme 1. L is stable at room
temperature without decomposition and is soluble in most common organic solvents but
1
13
insoluble in water. H and C NMR spectra of the ligand are presented in figures 1 and
1
2
, respectively. In the H NMR spectrum, aromatic protons are observed at δ 7.28–8.02
ppm as multiplets. A doublet at δ 8.33 ppm and a triplet at δ 8.06 ppm in 2 : 1 ratio were
assigned to pyridine protons. Benzene ring protons were observed at δ 7.28–7.89 ppm.
1
3
Aliphatic protons were observed at δ 0.71–4.73 as multiplets. In C NMR spectrum of
the ligand, aliphatic C shifts were δ 13.48–44.64 ppm. Aromatic carbon shifts were δ
1
13
1
10–151 ppm. Both H and C NMR spectra of the ligand showed that there was no
significant organic impurity in the sample.
The ESI spectrum of L in MeOH is given in figure 3 and showed signals at m/z 424
+
+
(
100%) and 446(15%) assigned to [L]H and [L]Na , respectively. There are two higher
+
+
mass peaks at m/z 847(15%) and 869(10%) assigned to [(L) + H] and [(L) + Na] , respec-
2
2
tively.
N-butylation of benzimidazole ring was further confirmed by IR spectroscopy. In the
−
1
spectrum of bzimpy, a broad band at 3193 cm assigned to ν(N–H) was observed. This
−
1
band disappeared in the spectrum of L and a new band at 2960–2930 cm assigned to
ν(C–H)(alkyl) was formed. The ν(C=N) vibration was observed for both bzimpy and L at
−
1
1
601 and 1595 cm , respectively.
3
.2. Synthesis of [Cu(L) ](ClO ) ] and [Cu(L)(bipy)](ClO )
4 2
2
4 2
[
Cu(L) ](ClO ) ] was obtained by 2 : 1 (L : Cu) reaction of L and Cu(ClO ) ·6H O in
2 4 2 4 2 2
MeOH. The reaction of one equivalent of L with one equivalent of Cu(ClO ) ·6H O in the
4
2
2
presence of one equivalent of 2,2′-bipyridine (bipy) results in a mononuclear complex [Cu

2
384
M. Kose
+
N
N
N
N
N
N
Cu
N
.
ClO4
N
N
N
Mw: 1008.35
m/z: 1008.36
+
2+
N
N
N
N
N
N
N
N
N
N
N
.
ClO4
Cu
Mw:585.12
m/z: 585.11
Cu
N
N
N
N
+
Mw: 909.42
m/z: 454.70
N
N
N
Cu
N
N
Mw: 486.09
m/z: 486.17
+
N
N
N
N
N
N
N
N
N
N
Mw: 394.49
m/z: 394.20
Mw: 338.38
m/z: 338.14
2 4 2
Scheme 2. Mass fragmentation pattern of [Cu(L) ](ClO ) ].

Cu(II) benzimidazole complexes
2385
2 4 2
Figure 4. ESI mass spectrum of [Cu(L) ](ClO ) ] (top), observed and theoretical isotope distribution (bottom).
(
L)(bipy)](ClO ) . Both complexes are soluble in MeOH, EtOH, acetonitrile, DMF, and
4 2
DMSO, slightly soluble in chloroform and dichloromethane and not soluble in water and
diethyl ether. The elemental analysis data are in agreement with calculated values.
−
1
IR spectra of the complexes are similar, and bands at 2960–2871 cm can be attributed
to aliphatic ν(C–H). The ν(C=N) vibrations for [Cu(L) ](ClO ) ] and [Cu(L)(bipy)](ClO )
4 2
2
4 2
−
1
were observed at 1599 and 1601 cm , respectively. Two strong stretches at 1073–620 and
088–622 cm were assigned to ν and ν of perchlorate for [Cu(L) ](ClO ) ] and [Cu(L)
3 4 2 4 2
−
1
1
(
bipy)](ClO ) , respectively.
4 2

2
386
M. Kose
In ESI mass spectra of the complexes, signals due to single and doubly charged ions
were observed for both complexes. In the mass spectra of [Cu(L) ](ClO ) ] (figure 4), the
2
4 2
signal at m/z 1008 (65%) was assigned to the singly charged complex cation [Cu(L) ]
2
+
(
ClO ) . Additionally, the signal at m/z 454 (100%) was assigned to the doubly charged
complex cation [Cu(L) ] . Mass spectrum fragmentations of [Cu(L) ](ClO ) are assigned
4
+
2
2
2
4 2
in scheme 2. Mass spectrum of [Cu(L)(bipy)](ClO ) showed signals at 742.69(35%), 321
4
2
+
2+
+
(
100%), and 486(10%) assigned to [Cu(L)(bipy)](ClO ) , [Cu(L)] , and [Cu(L)] ,
4
respectively.
UV–vis absorption spectra of the complexes were investigated from 200 to 800 nm in
−
5
MeOH (10 M). Bands at 400–343 nm can be attributed to n–π* transitions of the azome-
thine (C=N) groups. The bands at 344–270 nm may be assigned to π–π* transitions of aro-
matic rings. There are also absorption band shoulders for both complexes at 400–413 nm
2 4 2
Figure 5. TGA–DTA curves for [Cu(L) ](ClO ) ].
4 2.
Figure 6. TGA–DTA curves for [Cu(L)(bipy)](ClO )

Cu(II) benzimidazole complexes
2387
2+
Figure 7. Perspective view of [Cu(L)(bipy)] ; hydrogens, DMF and perchlorate ions are omitted for clarity.
assigned to M → L charge transition. No d–d transitions were observed for the complexes
at this concentration.
Thermal studies of the complexes were performed under nitrogen from 20 to 1000 °C.
TGA–DTA curves for complexes are shown in figures 5 and 6. Decompositions of the com-
plexes resemble each other, starting at 310 °C. Main weight losses were from 340 to
4
60 °C. Then, weights of the samples decreased slightly to 1000 °C. For both complexes,
all organic moieties decompose at 1000 °C leaving the CuO as the final decomposition
product.
3
.3. Molecular structure of [Cu(L)(bipy)](ClO ) ∙DMF
4 2
Single crystals suitable for X-ray diffraction were obtained by slow diffusion of diethyl
ether into a DMF solution of the complex and the complex was found to crystallize as [Cu
2
+
(
L)(bipy)](ClO ) ·DMF. Perspective view of [Cu(L)(bipy)] is shown in figure 7. The com-
4 2
plex crystallizes in the triclinic crystal system, P-1 space group with unit cell parameters a
9.4101(6), b = 11.0932(7), c = 20.5323(12) Å, α = 93.8370(10), β = 100.1520(10), γ =
=
3
9
5.6090(10)°, V = 2091.9(2) Å , and Z = 2 (final refinement value R = 0.0375). The asym-
2
+
metric unit contains one complex cation [Cu(L)(bipy)] , two uncoordinated perchlorates,
and one DMF solvate.
A geometry parameter τ, τ = (β – α)/60 where β and α are the two largest angles (β > α),
provides a measure of the degree of square pyramidal (SP) versus trigonal bipyramidal
geometry. For an ideal SP, τ is zero and for an ideal trigonal bipyramid τ becomes 1.0 [25].
In [Cu(L)(bipy)](ClO ) ·DMF, the largest angles within N2, N3, N4, and N6 are β = 175.75
4
2
(7)° for N3–Cu1–N6 and α = 157.03(7)° for N2–Cu1–N4. Thus, τ is (175.75–157.03)/60 =
0
.31. This indicates that the geometry around Cu(II) is distorted SP. Four nitrogens (N2,
N3, N4 and N6) are located at the equatorial plane and N7 of bipy is located at the axial
position. Cu1–N(7) (axial position) distance of 2.2540(19) Å is longer than Cu1–N dis-
tances at the equatorial plane (table 2). Moreover, there is a weak interaction between cop-
per and O(6) of a perchlorate at 3.125 Å, respectively; dramatically longer than those of
Cu–N bond distances.
There is evidence of π–π stacking interactions in the structure. One imidazole ring (N4–
C17–N5–C18–C23) is stacked with C7–C8–C9 edge of a neighboring molecule under sym-

2
388
M. Kose
Figure 8. π–π interactions within the structure. Hydrogens, DMF and perchlorate ions are omitted for clarity.
Figure 9. Packing plot for the complex showing π–π interactions within the structure. Hydrogens are omitted for
clarity.
metry operation of –x + 1, y, and z; C7 and C17 is separated by a distance of 3.217 Å
(
figure 8). Molecular packing of the complex is determined by π–π and CH(aromatic)…
OClO weak hydrogen bond type interactions as shown in figure 9.
3

Cu(II) benzimidazole complexes
2389

2
390
M. Kose

Cu(II) benzimidazole complexes
2391
The mononuclear complexes of L with CuCl ·2H O and Cu(NO ) ·3H O were previ-
2
2
3 2
2
ously prepared in our group [26]. It is informative to compare crystal structures of reported
Cu(L)Cl ]·2MeOH and [Cu(L)(NO ) ] with [Cu(L)(bipy)](ClO ) ·DMF. In the structures
[
2
3 2
4 2
of both published complexes ([Cu(L)Cl ].2MeOH and [Cu(L)(NO ) ]) and [Cu(L)(bipy)]
2
3 2
(
ClO ) ·DMF, the Cu(II) ions are five-coordinate with distorted square-pyramidal geometry
4 2
and they have similar Cu-donor distances. Trigonality indices (τ) are 0.105 and 0.0023 for
Cu(L)Cl ]·2MeOH and [Cu(L)(NO ) ], respectively [26]. In the structures of [Cu(L)
[
2
3 2
Cl ]·2MeOH and [Cu(L)(NO ) ], chloride and nitrate coordinate.
2
3 2
3
.4. Antimicrobial activity studies
Antimicrobial properties of the complexes were investigated against the bacteria and yeasts
(
(
B. subtilis and B. cereus (as Gram(+) bacteria); E. coli, E. aerogenes, and K. pneumoniae
as Gram(–) bacteria); and S. cerevisiae, C. utilis, and C. albicans (as yeasts). The diffusion
agar technique was used to determine the antimicrobial activity of the complexes. The
results of the microbial screening of the complexes are given in table 3.
The complexes show activity against all tested bacteria compared with Ampicillin 10 μg
under identical experimental conditions. Both complexes exhibit similar antimicrobial activ-
ity against bacteria and yeasts studied. The effect of the complexes on K. Pneumonia is less
than the other bacteria studied. The complexes are also active against yeasts used in this
study (S. cerevisiae, C. utilis, and C. albicans). The complexes show considerable anti-
fungal activity against S. cerevisiae, C. utilis, and C. albicans compared with Nystatin
1
00U (antifungal). The complexes are more effective on S. cerevisiae than C. utilis and C.
albicans under identical experimental conditions.
MIC values indicated that both complexes are active at low concentration against bacteria
and yeasts studied (table 4). However, antibacterial and antifungal activities of the com-
plexes are much less than Ampicillin (standard antibiotic) and Nystatin (antifungal) (table
−
1
4
). Both complexes showed the lowest MIC value of 200 μg mL against B. subtilis, B.
cereus, E. coli, E. aerogenes, and S. cerevisiae. [Cu(L) ](ClO ) exhibits higher activity
2
4 2
against K. pneumonia, C. utilis, and S. cerevisiae than [Cu(L)(bipy)](ClO ) ·DMF under
4
2
identical experimental conditions. Both complexes were more effective on E. coli and
B. subtilis than simple CuCl and Cu(ClO ) salts (table 4).
2
4 2
4
. Conclusion
Two copper(II) complexes of a benzimidazole ligand (L) were synthesized and character-
ized by spectroscopic and analytic methods. Molecular structure of [Cu(L)(bipy)](ClO4)2
was determined by single-crystal X-ray diffraction. The complexes were screened for
in vitro antibacterial and antifungal activity of B. subtilis and B. cereus (as Gram(+) bacte-
ria); E. coli, E. aerogenes, and K. pneumoniae (as Gram(–) bacteria); and S. cerevisiae, C.
utilis, and C. albicans (as yeasts). The complexes show moderate antibacterial and anti-
fungal activities against bacteria and yeasts used.

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M. Kose
Supplementary material
Crystallographic data have been deposited with the Cambridge Crystallographic Data
Center, CSD reference for [Cu(L)(bipy)](ClO ) ∙DMF is 984504. Copies of this information
4
2
can be obtained from The Director, CCDC, 12 Union Road, Cambridge, CB2 1EZ, UK
Fax: +44 1223 335033; Email deposit@ccdc.cam.ac.uk or http://www.ccdc.cam.ac.uk).
(
Acknowledgements
The author is grateful to the Department of Chemistry, Loughborough University for pro-
viding laboratory and analytical facilities. The author wishes to thank Prof. Vickie McKee
for allowing the use of the X-ray diffractometer and Prof. Metin Dığrak for antimicrobial
studies.
References
[
1] T.M. Kalyankar, S.S. Pekamwar, S.J. Wadher, P.S. Tiprale, G.H. Shinde. Int. J. Chem. Pharm. Sci., 3, 1
2012).
(
[
[
[
[
2] K.K. Mothilal, C. Karunakaran, A. Rajendran, R. Murugesan. J. Inorg. Biochem., 98, 322 (2004).
3] V. Klimešová, J. Kočí, M. Pour, J. Stachel, K. Waisser, J. Kaustová. Eur. J. Med. Chem., 37, 409 (2002).
4] K.F. Ansari, C. Lal. Eur. J. Med. Chem., 44, 4028 (2009).
5] E. Lukevics, P. Arsenyan, I. Shestakova, I. Domracheva, A. Nesterova, O. Pudova. Eur. J. Med. Chem., 36,
507 (2001).
[
[
6] S. Özden, D. Atabey, S. Yildiz, H. Göker. Bioorg. Med. Chem., 13, 1587 (2005).
7] Y. He, B. Wu, J. Yang, D. Robinson, L. Risen, R. Ranken, L. Blyn, S. Sheng, E.E. Swayze. Bioorg. Med.
Chem. Lett., 13, 3253 (2003).
[
[
8] M.A. Phillips. J. Chem. Soc., 2395 (1928).
9] M.R. Grimmet, A.R. Katritzky, C.W. Rees. Heterocycl. Chem., 5, 457 (1984).
[
[
[
[
[
10] X. Xu, Z. Xi, W. Chen, D. Wang. J. Coord. Chem., 60, 2297 (2007).
11] G. Muller, J.C.G. Bunzli, K.J. Schenk, C. Piguet, G. Hopfgartner. Inorg. Chem., 40, 2642 (2001).
12] A.Y.Y. Tam, W.H. Lam, K.M.C. Wong, N. Zhu, V.W.W. Yam. Chem. Eur. J., 14, 4562 (2008).
13] R. Boča, L. Dlháň, W. Linert, H. Ehrenberg, H. Fuess, W. Haase. Chem. Phys. Lett., 307, 359 (1999).
14] R. Boča, P. Baran, M. Boča, L. Dlháň, H. Fuess, W. Haase, W. Linert, B. Papánková, R. Werner. Inorg.
Chim. Acta, 278, 190 (1998).
[
[
[
[
[
[
[
[
[
[
[
[
15] B. Machura, A. Świtlicka, M. Penkala. Polyhedron, 45, 221 (2012).
16] W. Shuangxi, Z. Ying, Z. Fangjie, W. Qiuying, W. Liufang. Polyhedron, 11, 1909 (1992).
17] X.Q. Bai, S.H. Zhang. Acta Cryst., E65, 397 (2009).
18] M. Boča, R.F. Jameson, W. Linert. Coord. Chem. Rev., 255, 290 (2011).
19] Bruker. APEX2 and SAINT, Bruker AXS Inc, Madison, WI (1998).
20] G.M. Sheldrick. Acta Cryst., A64, 112 (2008).
21] A.W. Addison, P.J. Burke. J. Heterocycl. Chem., 18, 803 (1981).
22] V. McKee, M. Zvagulis, J.V. Dagdigian, M.G. Patch, C.A. Reed. J. Am. Chem. Soc., 106, 4765 (1984).
23] C.H. Collins, P.M. Lyne, J.M. Grange. Microbiological Methods, Butterworths, London (1989).
24] L.J. Bradshaw. Laboratory Microbiology, 4th Edn, Saundes College Publishing, Ft. Worth, TX (1992).
25] A.W. Addison, T.N. Rao, J. Reedijk, J. van Rijn, G.C. Verschoor. J. Chem. Soc., Dalton Trans., 1349 (1984).
26] M. Kose, M. Digrak, I. Gonul, V. Mckee. J. Coord. Chem., 67, 1746 (2014). doi: 10.1080/
0
0958972.2014.920502.
27] Z.B. Ou, Y.H. Lu, Y.M. Lu, S. Chen, Y.H. Xiong, X.H. Zhou, Z.W. Mao, X.Y. Le. J. Coord. Chem., 66, 2152
2013).
28] J.Y. Chen, X.X. Ren, Z.W. Mao, X.Y. Le. J. Coord. Chem., 65, 2182 (2012).
[
[
(